Geometric Approximation Theory

Main notation, definitions, auxillary results, and examples.- Chebyshev alternation theorem, Haar and Mairhuber's theorems.- Best approximation in Euclidean spaces.- Existence and compactness.- Characterization of best approximation.- Convexity of Chebyshev sets and sums.- Connectedness and stability.- Existence of Chebyshev subspaces.- Efimov-Stechkin spaces. Uniform convexity and uniform smoothness. Uniqueness and strong uniqueness of best approximation in uniformly convex spaces.- Solarity of Chebyshev sets.- Rational approximation.- Haar cones and varisolvencity.- Approximation of vector-valued functions.- The Jung constant.- Chebyshev centre of a set.- Width. Approximation by a family of sets.- Approximative properties of arbitrary sets.- Chebyshev systems of functions in the spaces C, Cn, and Lp.- Radon, Helly, and Carathéodory theorems. Decomposition theorem.- Some open problems.- Index.